ADSORPTION INDICATORS OF HEAVY METALS ON MODIFIED ADSORBENTS

ABSTRACT

This paper shows how to obtain high-stability carbon adsorbents from oil and oil waste gossypol and obtain hybrid adsorbents by modifying local bentonites. The data on the adsorption indicators of heavy metals modified adsorbents: adsorption in different pH environments, kinetic adsorption and desorption are also provided.

АННОТАЦИЯ

В данной статье показаны способы получения углеродных адсорбентов с высокой стабильностью из жирорастворимого госсипола и получения гибридных адсорбентов путем модификации их нативными бенонитами. Приведены также данные по показателям адсорбции тяжелых металлов модифицированными адсорбентами: адсорбции, адсорбционной кинетике и десорбции в различных pH средах.

Keywords: oil, coke, bentonite. Granules, carbon, tar, alkaline, gossypol, activation, modification, stability.

Ключевые слова: масложировых, кокс, бентонит, гранулы, углерод, гудрон, щелочь, госсипол, активация, модификация, стабильность.

Introduction

Various heavy metal ions (HM) present in industrial and domestic wastewater, particularly in wastewater ions of Pb(II) and Cu(II), are an urgent problem in many regions of the world. [1-3]. The main sources of HM poisoning of wastewater are waters of various industries and wastes of the mining and metallurgical industry. It is very important to develop an effective, inexpensive and environmentally friendly method to separate large amounts of this water and clean it from heavy metal ions. Solving these problems is desirable with environmentally safe, effective, and cheap adsorbents.

Gossypol tar from the oil industry was selected for the research work. [4]. It is possible to obtain a high stability carbon adsorbent from oil waste gossypol. Additional processing,  by changing bentonite, yields adsorbents with the potential for effective and rapid regeneration. [5].

Physical activation consists of removing additional substances from the substance using various physical methods (centrifugation, flotation, and filtering) without changing the composition of the substance. [6].

Acid, alkaline, and other substances are often used to activate chemicals. In this way, the coke is cleaned of various inorganic substances, activated and increased in porosity and surface area.

Method and materials

The waste oil was pyrolyzed  at 150-2000C for 3 hours until gas evolution was completed to activate Gossypol. The productivity of carbon adsorbent extraction from Gossypol resin was 40-50 per cent. It was activated for 3 hours with 0.1H of chlorine to eliminate various additives from pyrolyzed coke. After activation, the coke is washed with distilled water. [8].

The coal obtained from Gossypol tar was selected to change with adsorbents, and samples of various additives cleaned with high absorption properties were mixed with logon (LB) and shorsuv (ShB) bentonite. Logon bentonite (GLB) and Shorsuv (GShB) adsorbents were obtained by adding water to the mixture and activating it for 3 hours using a mixer with a heater. After the activation process was completed, each sample was dried to a moisture content of 30%. The activation process was carried out by placing 100 ml of 30% hydrogen peroxide solution in a 500 ml beaker and mixing 50 g of the sample with it at a temperature of 70°C until the end of gas evolution. After the activation process, the suspension was filtered to separate the adsorbent, and the filtrate was washed with distilled water and dried at 150°C for 180 minutes.The dried sample is converted into granules using a granulator.

Results and discussions

In order to study the adsorption of heavy metals by activated (GLB and GShB) adsorbents, Pb(II) and Cu(II) ions were selected from heavy metals and their concentration changes were determined in the AVS-1.1 voltammeter analyzer.

Studying the adsorption properties of the activated adsorbent for Cu (II) and Pb (II) at different pH values:

Adsorption characteristics of heavy metal adsorption in modified adsorbents at different pH values were studied.During the adsorption processes, sorption was carried out at pH 5.0 and 6.0 for Cu (II) and Pb (II).  For this, solutions of Cu(NO₃)₂ and Pb(NO₃)₂ salts (50 mg/l ~ 80 mg/l) were prepared. 0.1 N HNO₃ solution was added to the solutions to bring the pH to 5.0 and 6.0. 5 g of GShB and GLB were added to 500 ml of the prepared Cu(NO₃)₂ and Pb(NO₃)₂ solutions.

The solution was left at room temperature for 2 hours, then the adsorbents in the solution were separated by passing through a 0.50 μm filter.The amount of metal ions in the filtrate was checked using an AVS-1.1 voltammeter analyzer.

Metal concentration qe (mg/g) was calculated using the following formula:

q_e- amount of adsorption, C_i- metal concentration in the original solution, C_p- metal concentration in the filtrate, V- solution volume, M- adsorbent mass.

According to the results of the research, it was found that the sorption of metals in adsorbents increases up to pH 6 and then decreases. (Table 1).

This is consistent with the acid-base nature involved in metal binding as pH increases from 5 to 6. Also, in all adsorbents, Pb⁺² ions are adsorbed more than Cu⁺².Thus, the adsorption of metals on modified adsorbents is not directly related to their properties such as the size of the surface area and the total volume of pores, but to the acid-base interaction of chemical acids.

Table 1.

Adsorption of activated adsorbent for Cu (II) and Pb (II) at different pH values

It can be seen from Table 1 that at the same pH value (6), Pb ions in GLB and GShB are 127.4 and 137.6 mg/g, and the adsorption amount is ~5, 6 times higher than activated carbon, and pH is more than 6 It was found that adsorption decreases sharply with stretching.

Adsorption kinetics of Cu⁺² and Pb⁺² ions on activated adsorbents:

The adsorption kinetics of Cu⁺² and Pb⁺² ions in activated adsorbents (GLB and GShB) based on local bentonites and gossypol tar was studied. Studies (pH-6) were conducted. To study the adsorption kinetics of Cu (II) and Pb (II) ions on adsorbents, solutions of Cu(NO₃)₂ and Pb(NO₃)₂ salts (50 mg/l ~ 80 mg/l) were prepared.  0.1 N HNO₃ solution was added to the solutions to bring the pH to 6.0. 5 g of GShB and GLB were added to 500 ml of prepared Cu(NO₃)₂ and Pb(NO₃)₂ solutions.The adsorbent was left in the solutions for 10, 20, 30, 40, 50, 60, 90, 120 minutes, then the adsorbents in the solution were separated by passing through a 0.50 μm filter.The amount of metal ions in the filtrates was checked using an AVS-1.1 voltammeter analyzer. The concentration of metals qt (mg/g) was calculated using the following formula.:

q_t- amount of adsorption, C_i- metal concentration in the original solution, C_t- metal concentration in the filtrate obtained after the adsorption time, V- solution volume, M- adsorbent mass

According to the study results of the kinetics adsorption process of heavy metals on modified adsorbents, the main part of the adsorption of heavy metals on both adsorbents lasted for 10 minutes, which indicates that these adsorbents have a microporous structure and the presence of active centers in them. It can be seen that the saturation point has been reached after 40 minutes (Figure 1).

Figure 1. A) Adsorption kinetics of Cu⁺², Pb⁺² ions on GShB and GLB

Study of desorption properties of modified adsorbents.

It can be seen from the above experiments that GLB and GShB can be used in wastewater treatment using their high adsorption properties and hydrophobic properties. In addition to wastewater treatment with the help of GLB and GShB, it is also important to study their desorption properties. Taking this into account, GLB and GShB desorption characteristics of wastewater treatment from heavy metals (Cu+2 and Pb+2) were studied. Changes in their concentration were determined in the AVS-1.1 voltammeter analyzer.In order to study the desorption properties of GLB and GShB on heavy metals (Cu+2 and Pb+2), their working solutions of 50 mg/l were prepared, since the content of these metals in wastewater is very small. 5 g of granulated bentonite was added to 100 ml of the prepared solutions and stirred for 15 minutes using a mixer. Then, bentonite was separated from the solutions by passing through a 0.50 μm filter. The amount of heavy metals remaining in the obtained filtrate was checked by AVS-1.1 voltammeter analyzer.The process of desorption of heavy metals contained in the used bentonite was carried out with the help of 0.05 M HNO3 solution. For this, bentonite was added to a 0.05 M HNO3 solution at a ratio of 1/5 and mixed for 10 minutes. It was filtered from the solution and dried at a temperature of 200-250 ⁰С.

The desorption process was carried out up to 5 times. The conducted studies show that (Fig. 2) the adsorption process of GLB and GShB for heavy metals is almost the same up to the first 3 times, and in the subsequent stages, after 5 times, the adsorption decreases, and the modified granule state does not exist. it was determined that it will harden into a fine powder. It was also found that Cu⁺² (0.04-0.25 mg/l), Pb⁺² (0.04-0.6 mg/l)  remained in the filtrates.

Figure 2. Desorption of Cu⁺², Pb⁺² ions in A) GShB-3, B) GLB-3

Conclusion

The adsorption efficiency of modified adsorbents based on gossypol tar and local bentonites was Cu (85-90%), Pb (80-90%). Also, its desorption process up to 3 times is the basis for saying that as a result of modification of bentonite with gossypol resin, its chemical stability increases several times. Based on this, we can consider that it is possible to use them in the purification of wastewater from heavy metals.

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